PARIS — Are traditional bulky turbines the only way to capture the energy blowing in the wind? The answer, my friend, is apparently No.
Earlier this year, a team of scientists from Ecole Polytechnique and Paris Superior National School of Advanced Techniques (Ensta ParisTech) measured how a "simple" flag made of the right material can also be well-suited for the production of energy.
Over the last decade, researchers have been working on the possibility of producing power out of such undulations of a flexible membrane in water, another fluid, or in the air. Piezoelectric ceramics, which create tension when being deformed, are among the most promising materials.
According to the simulations published in Physical Review Applied, the more wind there is the more electricity it creates, though not proportionally because of the erratic undulations of the flag. Where it is interesting, however, is that for the first time, it highlights that the wind is not the only factor in the efficiency of the system; the type of circuit to which it is tied also has great influence. Sébastien Michelin, from l'Ecole Polytechnique, and Olivier Doaré, from Ensta ParisTech explain that "within certain conditions, the productivity can jump from 0.1 to 6%."
Thus engineers are now working on the fabric of flags but also on the composition of circuits. The mechanical and the electrical system are joined together. Thanks to that, even if completely down, a flag would still be able to produce a few electrons. "By influencing the flag dynamics with the electronic components so as to adapt to the wind conditions, we can make it work in many more cases," notes Michelin.
How many flags?
The team is optimistic, noting that making improvements to the electric circuits is not necessarily a complicated task. Christophe Eloy, researcher at Ecole Centrale in Marseille, points out that "they are not the first ones to have the idea to use flags but they are the first to have properly detailed the system."
In reality, these technologies, producing less than 1 watt, will not replace the wind turbines that produce a million times more than the flags. They will, however, be useful for recharging batteries, for example.
Many questions still need to answered; how many flags and in which position? If all of them were in synch, conditions would optimal. Unfortunately, Christophe Eloy and his collaborators showed in 2009 that if three flags were put right next to each other, only two flags would be waving and the one in the middle would stay motionless.